1. Field of the Invention
The present invention relates to a field emission display (FED) and, more particularly, to an apparatus and method for driving an FED device.
2. Description of the Conventional Art
Recently, demands on displays are increasing according to the rapid development of information communication technologies and the structures of displays are variably changing. For example, in an environment requiring mobility, a mobile information communication device such as a light, small and low power-consuming display is required, while when the display is used as a typical information conveying medium, a display with a large screen such as a CRT (Cathode Ray Tube), an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), a VFD (Vacuum Fluorescent Display) is required. Thus, the development for FEDs that can provide high resolution as well as having a reduced size and power consumption are being actively pursed.
The FED is receiving attention as a flat panel display for supporting next-generation information communications as it overcomes many shortcomings of currently developed or mass-produced flat panel displays (e.g., LCDs, PDPs, VFDs, etc.). The FED device has a simple electrode structure, can be operated at high speed such as the CRT, and has the advantage of being able to display a wide variety of colors, gray scale tones and provides high luminance.
Recently, FED devices having carbon nano tubes (CNTs) are being commonly used. The CNT is mechanically strong, chemically stable and has excellent in electron emission characteristics at a low degree of vacuum. By having a relatively small diameter (approximately 1.0˜scores of nm), the CNT has a superior field enhancement factor when compared with an emitter having a micro tip, and thus can emit electrons at low turn-on electric fields (approximately 1.0˜5.0V/μm). Thus, by applying the CNT to an FED device, a power loss and production unit cost of the FED device can be reduced.
A structure of the FED device having the CNT will now be described with reference to FIG. 1.
FIG. 1 is a sectional view showing the structure of a general FED device.
As shown in FIG. 1, a conventional FED device includes an upper glass substrate 10; an anode electrode 11 formed on the upper glass substrate 10; a phosphor layer 12 formed on the anode electrode 11; a lower glass substrate 1; a gate electrode 2 formed on the lower glass substrate 1; an insulation layer 3 formed on the gate electrode 2; a cathode electrode 5 formed on the insulation layer 3; a CNT (Carbon Nano Tube) 6 formed on the cathode electrode 5; and a counter electrode 4 electrically connected with the gate electrode 2 exposed through a via hole of the insulation layer 3 and formed on the same plane with the cathode electrode 5. The upper glass substrate 10 and the lower glass substrate 1 are disposed at the opposite side with a certain interval therebetween.
In order to drive the FED device, when a high voltage is applied to the anode electrode and a low voltage is applied to the gate electrode 2 and to the cathode electrode 5, electrons are emitted from the CNT 6, accelerated by the high field of the anode electrode 11, and then collide with the phosphor layer 12.
Since the counter electrode 4 and the cathode electrode 5 are formed on the same plane, electrons emitted from the CNT 6 move toward the counter electrode 4 and then move toward the phosphor layer 12 by the high field of the anode electrode 11.
However, since the high voltage applied to the anode electrode 11 affects the CNT 6, electron beams can be easily distorted to degrade the display quality and cross talk (interference) is caused among neighboring cells due to the distorted electron beams.
Therefore, in order to prevent the distortion of electron beams and concentrate electron beams into the cell, a mesh electrode is additionally formed.
FIG. 2 is a sectional view of an FED device having a mesh electrode in accordance with the conventional art.
As shown in FIG. 2, the FED device having a mesh electrode includes: an upper glass substrate 110; an anode electrode 100 formed on the upper glass substrate 110; a lower glass substrate 15; a conductive layer 20 formed on the lower glass substrate 15; an insulation layer 30 formed on the conductive layer 20; a cathode electrode 40 formed on the insulation layer 30; a CNT 50 formed on or near the cathode electrode 40; a gate electrode 25 electrically connected with the conductive layer 20 exposed through a via hole of the insulation layer 30; and mesh electrodes 70 supported by structures 60 formed on the cathode electrode 40 and on the gate electrode 25. The upper glass substrate 110 and the lower glass substrate 15 are disposed with a spacer 80 therebetween at a certain interval in a facing manner.
The structures 60 are made of glass, and the mesh electrodes 70 are formed on the structures 60. The mesh electrodes 70 are disposed at an upper side of the gate electrode 25 and the cathode electrode 40, thereby spreading and distortion of electron beams can be prevented.
When a high voltage is applied to the anode electrode 100 and a low voltage is applied to the cathode electrode 40, electrons are emitted from the CNT 50. At this time, a fixed amount of DC voltage is applied to the mesh electrodes 70.
The mesh electrodes 70 shields electric field generated by the anode electrode 100 so that the high voltage applied to the anode electrode 100 cannot affect the gate electrode 25 and the cathode electrode 40. Thus, electrons emitted from the CNT 50 are accelerated by the voltage applied to the mesh electrodes 70 and proceed toward the mesh electrodes 70. After passing through the mesh electrodes 70, electrons are accelerated by the anode electric field, and then, collide with the phosphor layer 90. Namely, the mesh electrodes 70 serve to concentrate electron beams into the cell.
However, since the insulation layer 30 with a dielectric component is positioned between the gate electrode 25 and the cathode electrode 40, electric charges are charged in the insulation layer 30, and as the electrons emitted from the CNT 50 collide with the mesh electrodes 70, electric charges are also charged not only in the mesh electrodes 70 but also in the structures 60 supporting the mesh electrodes 70, causing a problem that electron beams are distorted, and thus a leakage current is increased to increase power consumption.
In addition, it is difficult to drive the FED device due to the high voltage because of the electric charges charged in the insulation layer 30, the mesh electrodes 70 and the structures 60 supporting the mesh electrodes 70, and thus, the luminance of the FED deteriorates.
As mentioned above, the FED device has the following problems.
That is, since the electric charges are charged in the insulation layer of the FED device, electron beams are distorted.
In addition, since the electric charges are charged in the mesh electrodes and in the structures for supporting the mesh electrodes, a leakage current increase, and distortion of the electron beams causes cross talk (interference) among neighboring cells.
U.S. Pat. Nos. 6,169,372, 6,646,282 and 6,672,926 also disclose various conventional techniques of the FED device.